Abstract. During the POLARCAT summer campaign in 2008, two episodes (2–5 July and 7–10
July 2008) occurred where low-pressure systems traveled from Siberia across the
Arctic Ocean towards the North Pole. The two cyclones had extensive smoke
plumes from Siberian forest fires and anthropogenic sources in East Asia
embedded in their associated air masses, creating an excellent opportunity to
use satellite and aircraft observations to validate the performance of
atmospheric transport models in the Arctic, which is a challenging model domain
due to numerical and other complications.

Here we compare transport simulations of carbon monoxide (CO) from the
Lagrangian transport model FLEXPART and the Eulerian chemical transport model
TOMCAT with retrievals of total column CO from the IASI passive infrared sensor
onboard the MetOp-A satellite. The main aspect of the comparison is how
realistic horizontal and vertical structures are represented in the model
simulations. Analysis of CALIPSO lidar curtains and in situ aircraft
measurements provide further independent reference points to assess how
reliable the model simulations are and what the main limitations are.

The horizontal structure of mid-latitude pollution plumes agrees well between
the IASI total column CO and the model simulations. However, finer-scale
structures are too quickly diffused in the Eulerian model. Applying the IASI
averaging kernels to the model data is essential for a meaningful comparison.
Using aircraft data as a reference suggests that the satellite data are biased
high, while TOMCAT is biased low. FLEXPART fits the aircraft data rather well,
but due to added background concentrations the simulation is not independent
from observations. The multi-data, multi-model approach allows separating the
influences of meteorological fields, model realisation, and grid type on the
plume structure. In addition to the very good agreement between simulated and
observed total column CO fields, the results also highlight the difficulty to
identify a data set that most realistically represents the actual pollution
state of the Arctic atmosphere.